1. Field of the Invention
The present invention generally relates to a display apparatus, and more particularly to an apparatus for independently controlling the illumination of two visual indicators with a single output pin of an integrated circuit.
2. Description of the Related Art
Most electronic devices today, such as a printer, modem, computer, server, pager, phone, etc., utilize visual indicators to display various operational conditions of the device to the user. In the same conventional devices, each visual indicator is independently driven using separate pins of an integrated circuit (xe2x80x9cICxe2x80x9d). This type of conventional display apparatus is undesirable in that it is xe2x80x9cpin constrainedxe2x80x9d. In other words, an excessively large number of IC pins are required to drive a large scale display element or apparatus. Notably each additional pin in an application specific integrated circuit has a tangible cost associated to size and power characteristics of the IC package.
Another factor of a conventional display apparatus is that each visual indicator of the device typically requires a separate current limiting resistor. The use of additional current limiting resistors is undesirable because they increase the cost, size and the power consumption required by the IC package that supports them. In other words, as the number of current limiting resistors increase, so will the cost for an IC package that can accommodate the size and power constraints for operating the same.
Still another factor of a conventional display apparatus is that the amount of power used to illuminate each visual indicator does not change. Therefore, a lighter colored visual indicator is more difficult to see by a user when active than a darker colored visual indicator.
In summary, each additional pin or current limiting resistor required to drive the visual indicators of a conventional electronic device eliminates other possible functions that the pins of the IC for the display apparatus could be used for, or forces the use of larger and more expensive IC packages to drive the display apparatus. In addition, conventional display apparatuses can not be adjusted to provide more power to lighter colored visual indicators of a device so that they may be as recognizable as a darker visual indicator of the same display apparatus.
Accordingly, it would be beneficial to develop an improved display element or apparatus for an electronic device that: requires a single integrated circuit output pin to selectively drive or illuminate two visual indicators; is constructed with a single current limiting resistor to drive two independent visual indicators so that the power consumption, cost and size of the circuit for operating the same can be reduced; and can selectively supply more power to lighter colored visual indicators to increase their visibility.
In one embodiment of the invention an apparatus is provided for independently illuminating two independent visual indicators with a single control line. The apparatus includes two visual indicators, a logic circuit and an inverting amplifier. The two visual indicators connect in parallel with the cathode to anode direction of one indicator being opposite the other indicator. The inverting amplifier couples between the single control line of the logic circuit and a first and second end of the two indicators, wherein a combination of signals applied to two inputs of the logic circuit selectively creates a single output signal at the single control line to illuminate one of the two indicators.
In another embodiment of the present invention, a process is disclosed for controlling the illumination of two independent visual indicators with a single control line coupled to a logic circuit. The process includes simultaneously providing one of a HIGH and a LOW signal to a first and second input of the logic circuit to create one output on the single control line for controlling the illumination of one of the two indicators. A low signal applied to the first input fails to illuminate either of the two indicators, and a high signal applied to the first input illuminates one of the two indicators.